SHO driver¶

The SHO driver implements a classical simple harmonic oscillator (SHO) with a single frequency and dipole moment. It is provided by maxwelllink.mxl_drivers.python.models.SHOModel and ships with MaxwellLink for lightweight regression tests and benchmark scenarios.

Note

The SHO driver advances the classical phase-space variables \((q,\,p)\) generated by the Hamiltonian

\[H(q, p, t) = \frac{1}{2}\,\omega_0^{2}\,q^{2} + \frac{1}{2}\,p^{2} - \mu_{0}\,q\,\bigl(\widetilde{\mathbf{E}}(t)\cdot \mathbf{e}_{i}\bigr),\]

written in atomic units with unit mass. Here \(\mathbf{e}_i\) denotes the orientation unit vector of the dipole. The equations of motion are integrated with the velocity Verlet algorithm, and the emitted dipole current returned to Maxwell’s equations is

\[\frac{d}{dt}\langle \boldsymbol{\mu} \rangle = \mu_{0}\,p\,\mathbf{e}_{i}.\]

Requirements¶

No additional packages are required beyond MaxwellLink’s dependencies.
numpy (already bundled) is used for the velocity Verlet integration.

Usage¶

Socket mode¶

mxl_driver --model sho --port 31415 \
  --param "omega=0.242, mu0=187, orientation=2, p_initial=1e-2, \
           q_initial=0.0, checkpoint=false, restart=false"

Non-socket mode¶

mxl.Molecule(
    driver="sho",
    driver_kwargs={
        "omega": 0.242,
        "mu0": 187.0,
        "orientation": 2,
        "p_initial": 1e-2,
        "q_initial": 0.0,
    },
    # ...
)

Parameters¶

Name	Description
`omega`	Oscillator frequency in atomic units. Default: `2.4188843e-1`, corresponding to `1.0` in Meep units when `time_units_fs=0.1`.
`mu0`	Dipole-coordinate coupling prefactor \(\mu_{0}\) in atomic units, so that the instantaneous dipole is \(\mu(t)=\mu_{0}\,q(t)\); scales the emitted source amplitude. Default: `1.870819866e2`, corresponding to `0.1` in Meep units when `time_units_fs=0.1`.
`orientation`	Dipole orientation: `0` couples to `E_x`, `1` to `E_y`, `2` to `E_z`. Default: `2`.
`p_initial`	Initial momentum \(p\) of the oscillator in atomic units. Default: `0.0`.
`q_initial`	Initial position \(q\) of the oscillator in atomic units. Default: `0.0`.
`checkpoint`	When `True` write `sho_checkpoint_id_<n>.npz` after each step. Default: `False`.
`restart`	When `True` resume from the latest checkpoint if present. Default: `False`.
`verbose`	When `True` print field values and oscillator diagnostics each step. Default: `False`.

Returned data¶

time_au – Simulation time in atomic units.
energy_au – Instantaneous oscillator energy \(\tfrac{1}{2}\omega_0^{2} q^{2} + \tfrac{1}{2} p^{2}\) in atomic units.
mux_au, muy_au, muz_au – Dipole vector components (non-zero along the selected orientation) in atomic units.
p_au – Oscillator momentum \(p\) at the current step in atomic units.
q_au – Oscillator position \(q\) at the current step in atomic units.

Notes¶

The driver exposes a deterministic analytic evolution; see tests/test_sho/test_singlemode_sho_energy_conservation.py for a single-mode strong-coupling energy-conservation reference.
This driver is intended for demonstration and benchmarking. For productive classical molecular dynamics, prefer the LAMMPS or DFTB+ socket driver, or the ASE Python driver.